Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries the full behavioral burden and does a good job on the commercial/access traits: $0.002 USDC on Base or Solana, no account or API key required, and failed calls are not charged — unusually valuable for a paid endpoint. It also discloses the upstream data source and the literal URL. It does not mention rate limits, latency, or result-size behavior, so it is not a 5.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

A single dense line with no filler; leading with 'Paid.' and the price puts the cost decision in front of the agent before the data description, which is the right ordering. The trailing URL is used efficiently. Slight density cost — price, payment rails, refund policy, and data spec are all crammed into one run-on string.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a paid, no-annotation, no-output-schema data endpoint, the description covers what is fetched, what it costs, how to pay, and that failures are free — the essentials. What is missing is any indication of the response shape (rows?? per-pool objects?) and whether sort/limit affect billing, which matters more here because there is no output schema to lean on.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, and the schema already documents sort (tvl/apy), limit (1-100, default 20), and min_tvl_usd (default 100000). The description adds no parameter-specific meaning beyond mentioning that APY and TVL are present in results, which only loosely hints at sorting. Baseline 3 is appropriate when the schema does the work.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific resource and scope: yield pools for the single protocol 'mellow-core', across chains, with the exact fields returned (APY, TVL, 7d APY change) and the data source (DefiLlama). That clearly separates it from the buy_yields_chain_*, buy_yields_token_*, and other buy_yields_protocol_* siblings. It stops short of a clean verb-first phrasing ('Paid. Live DeFi yields for...' is a noun phrase), which keeps it from a 5.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is only implied by the embedded protocol name: an agent must infer that this tool is for mellow-core protocol-level yields rather than chain-level (buy_yields_chain_base) or token-level aggregation. There is no explicit 'use this when' or 'use X instead when' sentence, and no statement about how it relates to buy_yields_top or buy_yields_stablecoins. The 3 reflects a selector that works from the name alone but is never stated.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.